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BIG PHYSICS, BIG QUESTIONS –

Young turtles’ oily breakfast sticks in the throat

By BERNIC WUETHRICH

One of the first things a newly hatched loggerhead turtle is likely
to taste as it begins its life in the sea is tar. As each generation of
Florida’s loggerheads swims out into the Atlantic, the young turtles encounter
‘fronts’ made up almost entirely of tar balls, says Blair Witherington,
a biologist at the Florida Marine Research Institute. After trailing the
turtles at the start of their journey, he found that more than half had
tar caked in their jaws, while in a third the tar had reached their stomachs.
Lacking dietary discrimination, says Witherington, the turtles bite at anything
that floats by, whether it is animal, vegetable or mineral.

The southeast coast of the US is the second-largest loggerhead nesting
area in the world. Each year, more than 35 000 turtles lay their eggs along
the coast from Florida to South Carolina. In July, the young break out of
their eggs, dash across the sand, and set out for the ocean in a frenzied
swim lasting at least 30 hours. Until now, little was known about what happened
to the turtles once they made it out to sea.

But last summer, Witherington went in search of the young turtles in
the offshore zone where currents converge and produce ‘fronts’, narrow bands
of floating sargassum weed and debris. These frontal zones, which lie between
10 and 60 kilometres from the coast, border the western edge of the Gulf
Stream, which carries the turtles north on the first leg of their journey
around the Atlantic.

At the frontal zones, Witherington came across a turtle roughly every
five minutes. After their energetic swim, the hatchlings had entered a lazier
stage of life, basking at the surface. Witherington netted 160 turtles,
gave each a quick physical examination and washed out the stomach contents
of 50 of them to see what they had been eating. The first hint that all
was not well came when he removed a stomach tube and found it caked with
tar.

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Given the turtles’ environment, he was not surprised by what he found,
Witherington told the 14th Annual Sea Turtle Symposium held last week in
South Carolina. ‘Some of the frontal zones contained nothing but lumps of
tar lined up just like you usually see sargassum.’

A loggerhead’s throat is lined with spiky papillae that point towards
the stomach. When a turtle eats, it squeezes its throat muscles to strain
off the water before it swallows. The papillae prevent slippery foods such
as jellyfish from being expelled with the water. When the turtle swallows
a ball of tar – and squeezes – the tar clogs up the papillae and ruins its
ability to strain off seawater. Young turtles can excrete salt, but if
they swallow salt faster than they can get rid of it, they become dehydrated
and die. ‘They could be dying by the hundreds of thousands and no one would
know,’ says Witherington.

Witherington also found large amounts of plastic and caulking material
in the turtles’ stomachs. Clumps of tar and plastic could block the gut
and cause malnutrition.

The turtles’ normal diet consisted mostly of jelly-like invertebrates,
larval shrimps and crabs, and sargassum. Other types of plant, insects and
flatworms were also found. The turtles seemed to prefer slow-moving and
visually interesting food items.

Sea turtles have been travelling the oceans for 200 million years. ‘They
evolved in a world that favoured adventurous sampling of cuisine,’ says
Witherington. ‘They just don’t have the culinary savvy to distinguish the
unwanted from the innocuous.’